Oscillation generator



Jan. 14, 1930. L, WOLF 1,743,178

OSCILLATION GENERATOR Filed Feb. 4, 1929 INVENTOR 8 /a lesrjifiya 5 z /4 BY A'TToRNEY Patented Jan. 14, 1930 UNITED STATES LESTER J. WOLF, OF PITTSBURGH, PENNSYLVANIA, ASSIGNOR T0 WESTINGHOUSE ELECTRIC & MANUFACTURING COMPANY, A CORPORATION OF PENNSYLVANIA OSCILLATION GENERATOR Application filed February 4, 1929. Serial No. 837,476.

My invention relates to oscillation generators, and it has particular relation to vibratory frequency-controlling devices adapted for use in such generators to maintain constant the oscillation-frequency thereof.

The rapid increase in the number of radio transmitting stations operating in restricted areas renders it obligatory that the transmitting-frequencies of such stations shall be kept spaced apart at least ten kilocycles in order to obviate interference between them. It is also necessary that each station shall keep strictly to its assigned frequency and, for this purpose, the majority of transmitting stations now utilize oscillators controlled, as to frequency, by piezo-electric crystals.

Unfortunately, piezo-electric crystal sections are quite prone to break during use,

especially if subjected to abnormal potentials and, for that reason, oscillation-controlling devices of more sturdy character are often desired. It has, accordingly, been suggested that a tuning fork, excited and kept in oscil- I lation at its natural period by suitable means,

might advantageously be substituted for the customary quartz crystal-section. The patent to Horton, No. 1,560,056, illustrates and describes several possible ways of utilizing a tuning fork in an oscillation-generator system, and it. also discloses a particular mounting device for the tuning fork per se.

I have noted, however, that systems of the general type disclosed in' the Horton patent do not always operate in an entirely satisfactory manner 'to deliver a constant frequency. Among the causes of irregular operation may be mentioned direct coupling between the driving and controlling coils associated with the fork, partial oscillations of the fork itself, oscillations of the supporting device and temperature variations.

It is, accordingly, an object of my invention to provide a tuning-fork holder wherein means are incorporated for preventing direct coupling between a plurality of driving and controlling coils associated with the fork.

Another object of my invention is to provide a. tuning-fork holder that shall protect a'fork supported thereby against temperature variations.

Another object of my invention is to pro vide a novel combination between a tuning fork, a support therefor, and adjustable driving and controlling coils for maintaining the fork in oscillation at its natural period.

Another object of my invention is to provide a novel combination of the type described that shall be capable of functioning as a filter for differentiating between electrical oscillations at the natural period of the fork and other oscillations atheterogeneous frequencies.

In practicing my invention, I suspend a tuning fork in the interior of a massive nonmagnetic, metallic, housing provided with adjustable electro-magnetic means for applying driving impulses to the tines of the forks, and

also for deriving electrical potentials proportional to the oscillations thereof.

The housing further comprises means for preventing magnetic interaction between the tines of the fork and for preventing magnetic and electrostatic interaction between the driving coils associated therewith, Such means is preferably constituted by a shield comprising a plurality of thicknesses of magnetic and non-magnetic material maintained in firm contact with each other and interposed between the tines of the fork and, consequent ly, between the aforesaid coils. The shield may or may not be an integral part of the fork-housing.

The novel features that I consider characteristic of my invention are set forth with particularity in the appended claims. The invention itself, however, both as to its organization and its method of operation, to-

vibratory end of which is tightly clamped between two massive blocks 2 and 3 of nonmagnetic metal. A plurality of tiefrods 4 and 5 extend through aligned transverse openings in the clamping blocks, each tie rod preferably being provided with a lockwasher 6 and a nut 7.

The clamping blocks 2 and 3 rest upon the upper end of a fork-housing constituted by two blocks 8 and 10 of non-magnetic material, such as brass or the like, having vertically disposed channels 11 and 12 therein in which the tines 13 and 14 of the tuning fork depend. A-sheet 15 of magnetic material is interposed between the blocks constituting the fork-housing and is held rigidly in position by a plurality of assembly bolts 16 that extend transversely through aligned openings in the said blocks.

Vibratory movement of the fork and the associated clamping blocks with respect to the fork-housing is prevented by four or more tie-bolts 17 the lower ends of which are imbedded in the housing, and the upper ends of which extend through vertical openings in the clamping blocks.

The side walls of the fork-housing that intersect a plane passing through both of the depending tines of the fork are each provided with a relatively large threaded opening 20 that communicates with one of the vertical channels in which a tine of the fork is disposed.

Each of the openings 20 is internally threaded to' accommodate an externally threaded cylindrical member 21 provided with an interior partition 22 on which a driving magnet 23 is mounted. The terminals of the driving magnet are connected to a plurality of contact elements 24 that are mounted upon, and project rearwardly from,

a circular insulating plate 25 fitted into the outer end of the cylindrical member 21.

The pitch-0f the threads cut upon the exterior of the cylindrical member 21 is pref-.

erably quite small in order that the space between the cores of the driving magnet and the tine of the fork associated therewith may be adjusted with nicety. The adjustment, when once made, is prevented from changing by a set-screw 30 that may be screwed down against the cylindrical member.

When a device such as I have described is utilized in any of the circuits illustrated in the Horton patent, previously referred to, or for any other pur ose that necessitates the frequency of the ork being held to within .01 per cent of its natural period it must be kept at a constant temperature. Preferably, the device is enclosed in a cabinet, or the like, provided with a heating device, a thermostat andfmeans for causing a constant current of heated air to pass over and around the fork-housing. No specific form of 'cabi net is illustrated, since its construction should be fairly obvious to anyone skilled in the art.

Inasmuch as the massive blocks that enclose the fork have a high thermal-lag, the fork itself, after it has once assumed the temperature of the blocks, will be effectively protected against rapid changes in tempera- 'ture of the surrounding air; This characteristic of my improved fork-holder is extremely important in that it obviates the necessity of adjustingthe thermostat to operate within close limits.

The bimetallic shield, constituted by the like, wherein it is necessary to differentiate I between an incoming control-frequency and a plurality of heterogeneous frequencies occasioned by static, by interfering signals, or by other disturban ea In such systems, the incoming controlequency, together with other frequencies that have accompanied it through the amplifying apparatus, is applied to one of the driving coils associated with a fork tuned to the said frequency. The other driving coil is interposed in the input circuitof an amplifying device and serves to impress the control-frequency thereon just so long as the fork is maintained in the 'vibratory state by the incoming frequency. The fork, by reason of the fact that its oscillations persist for a short space of time, even in the absence of excitationyis able to both bridge over the periods when the reception of the control-frequency is interrupted and to prevent any interfering frequencies from being applied to the subsequent amplifier.

Many additional advantages of my invention, as well as modifications thereof, will be apparent to those skilled in the art to which it pertains. My invention, therefore, is not to be restricted to the specific embodiment chosen for purposes of illustration but is to be limited only by prior art and by the spirit of the appended claims.

I claim as my invention:

1. In combination, a tuning fork, a support therefor, and shielding means interposed between the tines of the fork.

2. In combination, a tuning fork, a support therefor, and metallic shielding means interposed. between the tines of the fork.

3. In combination, a tuning fork, a support therefor, and bimetallic shielding means interposed between the tines of the fork.

4. In combination, a tuning fork, a support therefor, and metallic shieldm means interposed between the tines of the ork, a portion of said shielding means being integral with said support.

5. In combination, a tunin fork, a support therefor, and bimetallic shi ding means interposed between the tines of the fork,a portion of said shielding means being integral with said su port.

p 6. In com mation, a-tuning fork,'a support I therefor constituted by a blocks, means for clamp g said blocks together, and shielding means interposed between said blocks.

7. A supporting device for a comprising a plurality of massive blocks hav ing openings therein for accommodating the tines of a fork and means for clamping said,

blocks together.

8. A supporting device for a tuning fork comprising means for clamping the fork and L means for shielding the fork against tempera ture variations.

9. A supporting device for a tuning fork comprising means for clamping the fork, means for shielding the fork against tempera ture variations, means for sub ecting the fork to magnetic influences and means for preventing ma etic interaction between the tines of the ork.

10. In combination, a tuning fork, means for subjecting the fork to magnetic influences, means for deriving electric potentials corresponding to fork-vibrations, and means for preventing interaction between said subjecting means and said derivingmeans.

In testimony whereof, I ave hereunto subscribed my name this 25th day of- January 1929.

- LESTER J. WOLF.

p'llurality of massive tuning fork' 

